The invention concerns a method of steering a vehicle, particularly an articulated vehicle, in which a valve element of a main valve is moved so that it releases or closes connections between a supply connection arrangement and a working connection arrangement in dependence of a steering direction and a steering angle.
In such a method, the driver specifies the steering angle, for example by means of a steering handwheel or a joystick. Depending on the specified steering angle, the valve element, for example a valve slide or a rotary valve slide is moved so that it releases a flow path for hydraulic fluid, which can accordingly reach a steering motor, for example a double-acting cylinder, from a pump. For finishing the steering process, either a measuring motor can be provided, which closes the opening released by the valve element by letting a second valve element follow, or the driver can return the steering angle sensor to the neutral position, so that the valve element closes. To make the invention better understood, the invention will in the following be explained on the basis of the latter example.
In articulated vehicles, the driver usually sits in the area of the articulation point, that is the point of the vehicle, which is moved most in connection with a steering process. Accordingly, also the accelerations of the steering process are the largest here. In most cases, the acceleration in itself is not critical, that is, most people do not find it unpleasant. However, with the change of the acceleration, which should not exceed a certain value, it is different. This acceleration change is also called xe2x80x9cjerkxe2x80x9d. A too large jerk is a load for the body of the driver, which is found unpleasant during a steering movement, particularly when the jerk repeatedly changes its direction. Accordingly, the limitation of the jerk plays a certain role for the improvement of the driver comfort. For example, at the end of the steering process, it will be particularly unpleasant for the driver that after the end of the steering movement the vehicle swings back and forth around the articulation point. This namely means that the jerk swings correspondingly.
The invention is based on the task of increasing the comfort in connection with the steering.
In a process as mentioned in the introduction, this task is solved in that the movement speed of the valve element is controlled.
The movement speed of the valve element is a measure for, how fast the cross section of the flow path for the hydraulic fluid between the supply connection arrangement and the working connection arrangement can be changed. When the valve element is only moved slowly, this flow path can also only be opened or closed gradually, so that the corresponding acceleration change, including the jerk, is limited to certain values. These values can be set so that they are still found acceptable by a majority of persons from the planned user circuit, for example, construction workers. The modification of the movement speed of the valve element is a relatively simple measure. It can be made inside the main valve and requires no complicated control by means of auxiliary or side valves. The reason is that the movement of the valve element must be controlled anyway. An additional step is that not only the movement in itself, that is the position change of the valve element, but also the kind of change must be influenced.
Preferably, the valve element is electrically activated and the change of the electrical size decisive for the operation is limited. For example, the valve element can be directly moved electrically via a magnet arranged, the current then being limited. The valve element can also be moved electro-hydraulically, a hydraulic pressure firstly being built up or reduced by means of the electrical size. In this case, for example, the voltage of the drive, that is, the pump, can be changed. The change of such an electrical size is in many cases also relatively simply programme controlled, that is, by means of software.
It is also advantageous that the movement speed of the valve element is controlled in dependence of one or more of the following parameters:
Vehicle speed
Vehicle weight
Load distribution
Driver""s seat position
Driver profile
At high vehicle speeds, it may, for example, be required for security reasons to permit a higher movement speed of the valve element than at low speeds. When the vehicle has a high weight, meaning that the inertia is larger, it may however be expedient to keep the movement speed of the valve element at a low value. It may also be considered, how the vehicle is loaded or where the load is situated, respectively. This is particularly clear in connection with a shovel loader. When the shovel is loaded, a point of the vehicle having the largest distance to the rotating joint is provided with a relatively high inertia. Without countermeasures this would lead to repeated swings, particularly at the end of the steering process. When here the movement speed of the valve element can be influenced, such swings can be avoided and the jerk is reduced. The driver""s seat position may have influence on the feeling of the driver, for example, when the distance to the hinge point of the vehicle is changed. The closer the driver is to the hinge point of the vehicle, the more uncomfortable will the side acceleration be to him. Finally, driver profiles can be defined, which each driver can select for himself. Those profiles can then, when a certain driver takes over the vehicle, be read into a control, for example by means of a bar code or a magnetic card.
A preferred, simple way of influencing the movement speed of the valve element is to change the relation between the steering angle specification and the movement path of the valve element. For example, in one case it may be provided that a steering handwheel must be turned 2.75 times to get from the left stop to the right stop. In another case, the same steering movement may be specified to require 4.5 or even 5.5 rotations of the steering handwheel. Of course, this also applies when a joystick is used instead of a steering handwheel. This xe2x80x9ctransmissionxe2x80x9d can also be used partially, that is, for smaller steering angles, meaning that it is not necessary for the vehicle to be actually steered from one stop to the other.
In this connection it is particularly preferred that for the change of the movement speed, the time available between two positions of the valve element is set. The shorter this time is, the higher must the speed be. On the other hand, the valve element can work with a lower speed, when it has more time for the displacement. The time as parameter is relatively easy to monitor and preset.
In this connection it is preferred that in the course of time, the movement of the valve element is guided along a preset function. For example, the movement speed can be higher in the middle of a time interval than at the ends.
In a particularly preferred embodiment it is provided that the closing speed of the valve element is limited. Thus, only part of the movement of the valve element is influenced, namely the part, in which the valve element closes. This is usually the critical part, as here a more or less instantaneous closing may cause a high jerk and large swings. At the beginning of the steering movement, the inertia forces of the vehicle are usually sufficient to prevent the acceleration and the acceleration change, that is, the jerk, from being too high.
Preferably, the position of the valve element is controlled in a closed control circuit. Thus, a reliable statement of the position of the valve element is continuously available, and the movement speed is accordingly relatively easy to control.